Small Gods by Terry Pratchett

Small Gods is one of the two standalone novels in the Discworld series. I had never read anything by Pratchett and before I dove right in I decided I'd dip my toes in. Small Gods centers around a single PoV character named Brutha who is the one true believer in the Great God Om who remains. As a result of a dearth of true believers, despite being the only god allowed in a rather large empire, Om is now trapped in the body of a lowly turtle and will need a nobody named Brutha to help reclaim his place in the pantheon of gods.